Our purpose is to investigate the interplay between convective flow (ventilation and circulation) on one hand and 02 uptake and C02 output on the other, with specific emphasis on: 1) situations where a decrease in convective flow may limit 02 supply or C02 elimination, 2) mechanisms by which 02 and C02 exchange affect convective flow, and 3) interaction between ventilation and circulation. The five projects constituting this program deal with 1) effects of gravity on the interaction between air and blood flow in the lungs, 2) effects of ventilation and cardiac output, 3) ventilatory response to C02 load, 4) local circulation and possible limitations in tissue oxygenation during exposure to 100% o2, and 5) redistribution of circulation when the ability to carry 02 is decreased by hemodilation. Interaction between the investigators is ensured by 1) the shared laboratories, equipment, and technical assistance, 2) the fact that most of them collaborate on several component projects, and 3) weekly research progress conferences.